In general, in fields which require security, a method based on a secret, which is shared with an encryptor, is adopted as means for certifying one's own authenticity.
For example, in IC cards, etc., which are used for electronic settlement, an individualized ID and secret information are stored in an IC in the card, and the IC card has a cipher processing function for executing authentication based on the ID and secret information. In another example, there is means for certifying authenticity of an SD card (trademark) in copyright protection of contents.